An object's scattering dyadic transforms incident plane waves to scattered far fields. In this paper, it is shown that characteristic modes can be calculated directly from a matrix representation of the scattering dyadic that may be constructed from only the solution of a series of plane wave scattering problems. Hence, the finite element method (FEM) [1]} or finite-difference time-domain method (FDTD) [2]} may be utilized, giving the opportunity to deal with arbitrary distributions of anisotropic dielectric and magnetic materials. An additional advantage is that the unknowns used in the underlying numerical method are decoupled from the degrees of freedom to express characteristic modes, , a studied object can be described and efficiently evaluated with millions of unknowns but the matrix representing the scattering dyadic used for characteristic mode eigenvalue decomposition can be significantly smaller, , hundreds of degrees of freedom for practical problems.
